The invention relates generally to dielectric compositions and, more particularly, to a method for producing barium titanate-based dielectric compositions using a heat treatment step.
Barium titanate-based compositions, which include barium titanate (BaTiO3) and its solid solutions, may be used to form dielectric layers in electronic devices such as multilayer ceramic capacitors (ILCCs). The barium titanate-based compositions are typically produced as micron-sized particles which may be further processed to form the dielectric layer. Such barium titanate-based particles may be formed in a variety of processes including hydrothermal processes, solid-state reaction processes, sol-gel processes, as well as precipitation and subsequent calcination processes, such as oxalate-based processes.
To enhance certain electrical and mechanical properties of the resulting layer, dopants may be added to the barium titanate-based compositions. Typically, the dopants are metallic compounds, often in the form of oxides. In some cases, dopant particles may be mixed and milled with the barium titanate-based particles to promote homogeneous distribution of the dopant throughout the composition. In other cases, the dopant may be coated upon the surfaces of barium titanate-based particles to provide homogenous distribution of the dopant materials without milling.
Dielectric layers of MLCCs are usually prepared from a dispersion of the barium titanate-based particulate composition in an aqueous medium which may also include a polymeric binder and/or dispersing agent. The dispersion, or slip, may be cast to provide a green layer of ceramic dielectric material. A patterned electrode material is then formed on the green layer to form a structure that is stacked to provide a laminate of alternating layers of green ceramic dielectric and electrode. The stacks are diced into MLCCs-sized cubes which are heated to sinter the particles of barium titanate-based material to form a capacitor structure with laminated, dense ceramic dielectric and electrode layers. During sintering, increased ceramic dielectric density is achieved as a result of the fusion and consolidation of the particles to remove pores between the particles and to form grains.
The miniaturization of electronic components and the desire to increase the volumetric efficiency of MLCCs has led to the production of dielectric layers of ever-decreasing thickness. To produce thinner layers, the barium titanate-based compositions must have sufficiently small and uniform particles which, in some cases, may have a relatively low density as compared to larger particles. Certain electrical properties may be inferior in compositions that include such small particles. For example, the dielectric constant may be lower and the dissipation factor may be higher for compositions having smaller particle sizes and/or lower particle densities. Therefore, the particle size must be balanced with the electrical properties when forming thin dielectric layers.
Accordingly, it is desirable to produce a barium titanate-based composition having a small particle size and desirable electrical properties.
The invention provides a method for producing barium titanate-based particulate compositions.
In one aspect, the invention provides a method for heat treating a barium titanate-based particulate composition. The method includes heating a barium titanate-based particulate composition at a temperature between about 700xc2x0 C. and about 1150xc2x0 C. to form a heat-treated particulate composition.
In another aspect, the invention provides a method for heat-treating a barium titanate-based particulate composition. The method includes heating a barium titanate-based particulate composition at a temperature and for a time sufficient to cause particle growth and insufficient to cause particle sintering thereby forming a heat-treated particulate composition.
Other advantages, aspects, and features of the invention will become apparent from the following detailed description.